Three-layer patterning processes are used in photolithography for semiconductors to pattern a semiconductor substrate. An exemplary three-layer patterning process 20 is illustrated in FIG. 1.
As shown in FIG. 1, a substrate 12, such as a silicon wafer, is provided with three layers: a photoresist layer 14, a middle layer 16, and an organic planarization layer 18. As shown in step 22, the layers may be sequentially applied by spin coating processes. In step 24, a lithography step patterns the photoresist layer 14. In step 26, a first fluorocarbon plasma etching step etches the portions of the middle layer 14 exposed through the pattern in the photoresist layer 14, transferring the pattern from the photoresist layer 14 to the middle layer 16. In step 28, a first oxygen plasma etching step removes the photoresist layer 14 and etches the portions of the organic planarization layer 18 exposed through the transferred pattern in the middle layer 16, transferring the pattern from the middle layer 16 to the organic planarization layer 18. In step 30, a wet etching step and/or a second fluorocarbon plasma etching step removes the middle layer 16 and etches the portions of the substrate 12 exposed through the transferred pattern in the organic planarization layer 18, transferring the pattern from the organic planarization layer 18 to the substrate 12. In step 32, a second oxygen plasma etching step removes the organic planarization layer 18, leaving behind only the patterned substrate 12.
In a typical process, the middle layer 16 may be removed by an acid-based wet etching solution. However, such a solution may cause damage to the exposed substrate 12 underneath. In particular, when the nodes of the transferred pattern are less than about 10 nm in width, such as nodes of 7 nm or 5 nm, the metal layers of the patterned substrate 12 become thinner, and are potentially more easily damaged by an acid-based etching solution.
To prevent damage to the substrate 12, an alkaline stripping solution may be used. An exemplary alkaline stripping solution is Standard Clean 1 (SC1), which is a high pH solution including deionized water, ammonium hydroxide, and hydrogen peroxide designed to remove organic films by oxidative breakdown and dissolution without damaging an underlying silicon wafer substrate. A typical SC1 solution is (by volume) 5 parts deionized water, 1 part 29% ammonium hydroxide, and 1 part 30% hydrogen peroxide. SC1 can be diluted to different concentrations, in some exemplary embodiments, dilute SC1 contains as little as 10 parts, 20 parts, 30 parts, 40 parts, as great as 50 parts, 60 parts, 80 parts, 100 parts deionized water, 1 part 29% ammonium hydroxide, and 1 part 30% hydrogen peroxide. Ratios between hydrogen peroxide and ammonium hydroxide can also vary, in some other exemplary embodiments, dilute SC1 contains 60 parts deionized water, 1 part 29% ammonium hydroxide, and as little as 2 parts, 5 parts, 10 parts, as great as 18 parts, 20 parts, 30 parts, 50 parts 30% hydrogen peroxide. The typical processing temperature for SC1 stripping is from 70° C. to 80° C., however a lower temperature SC1 process, such as strippability at 65° C. or less, such as 25° C. to 65° C., would be desirable for less unwanted etching, easier process control and lower cost.
The use of typical oxysilane materials for the middle layer 16 is limited by their poor stippability in SC1 solutions. Typical oxysilane materials containing repeating —(Si—O)n— units enable good coating performance and optical properties and, due to the inherent stability and flexibility of the siloxane (Si—O—Si) bond, those coatings can provide multiple benefits including extraordinary thermal stability, chemical resistance, good adhesion, scratch and abrasion resistance, superior gap fill and planarization and excellent dielectric properties.
However, typical polymers or oligomers containing oxysilane groups tend to continue condensing or crosslinking following baking or curing processing steps. The continued reaction results in a relatively high number of condensed —(Si—O)n— units, which are relatively resistant to stripping by SC1 solutions and especially resistant to low temperature SC1 solutions.
Improvements in the foregoing are desired.